Twelve hundred and nineteen healthy, sexually active women and men, 18-39 years old, without HIV infection were enrolled in Francistown and Gaborone, Botswana. They were provided with free male and female condoms, repeated individualized risk-reduction counseling, diagnosis and treatment of sexually transmitted diseases, and women will be provided with a choice of effective family planning methods. In addition, volunteers were randomized to receive either Tenofovir and emtricitabine (in a single pill) or a placebo pill to take once a day. Volunteers were seen monthly for at least 12 months to monitor for side effects and toxicities and to test their HIV status. Persons who become HIV infected during the trial received ongoing supportive counseling, CD4 and viral load monitoring, education about HIV infection/disease, and access to HIV care including free antiretrovirals when clinically indicated. Volunteer safety was monitored by a local ethics committee, Centers for Disease Control Institutional Review Board (CDC IRB) and an independent data safety and monitoring board